A liquid or partially liquid material that moves in a system may collide with a surface (an impact surface) in the system. The collision with the impact surface may result in splashing and/or scattering of the material, and the splashing and/or scattering may result in contamination of objects near the impact surface. The contamination may be, for example, bits of material that are flung from the material as a result of the collision. The contamination of the object may result in the performance of the object and/or the entire system being degraded. For example, the system may include a mirror, and contamination of the mirror may change the reflective properties of the mirror. The mirror may be a mirror in an EUV light source, and the contamination may result in reduced amounts of EUV light being output by the source.
Extreme ultraviolet (“EUV”) light, for example, electromagnetic radiation having wavelengths of 100 nanometers (nm) or less (also sometimes referred to as soft x-rays), and including light at a wavelength of, for example, 20 nm or less, between 5 and 20 nm, or between 13 and 14 nm, may be used in photolithography processes to produce extremely small features in substrates, for example, silicon wafers, by initiating polymerization in a resist layer.
Methods to produce EUV light include, but are not necessarily limited to, converting a material that includes an element, for example, xenon, lithium, or tin, with an emission line in the EUV range in a plasma state. In one such method, often termed laser produced plasma (“LPP”), the required plasma may be produced by irradiating a target material, for example, in the form of a droplet, plate, tape, stream, or cluster of material, with an amplified light beam that may be referred to as a drive laser. For this process, the plasma is typically produced in a sealed vessel, for example, a vacuum chamber, and monitored using various types of metrology equipment.